Preformed coils offer the highest numbers of wires that can be packed inside a slot. The commonly known “form wound” coils refer to the coils with their conductors arranged in a rectangulae-shape for a rectangular coil layer. The coil layer is put into a rectangular slot in the stator core. The problem associated with the traditional form wound electric machine is that a rectangular slot may not be the best design. In fact, most of the small and medium size electric machines generally use a non-rectangular slot to obtain the best magnetic design of the stator punching. This results in the shape of a coil layer to be bigger at the bottom of a slot (lower layer) and smaller at the top of a slot (upper layer). The existing technology cannot put a form wound coil of this non-rectangular layers into a slot of a stator lamination stack with many distributed slots, because the big lower layer of the coil cannot go through the small opening of the slot. Therefore, only the relatively low fill-factor mush-wound coils are used. This invention overcomes the problems associated with the low fill-factor and preserves the performance advantages of an electric machine having a distributed-winding in the non-rectangular slots.
This new technology is not associated with the preformed concentric-wound coils that are used for the compressed powder poles of some electric machines that have less attractive performance than that of the electric machines with distributed windings and slots.